1. Field of the Invention
This invention relates to a method of monitoring accurately the wear of refractory lining walls of a blast furnace due to high temperatures and other factors and a temperature probe assembly used for the method.
2. Description of the Prior Art
The blast furnace is a high temperature metallurgical reactor for solid reducing agents such as iron oxide materials including iron ore and coke, which includes refractory walls and its surrounding iron shell. Drilling the iron shell and filling a refractory repairing material are however necessary every time the refractory walls are eroded or exfoliated in various points since the interior of the blast furnace is kept at a high temperature and constantly subject to falling impact and friction by the iron ore or coke. In the past, it was as a matter-of-fact impossible to monitor accurately the wear of the refractory walls and even the primitive procedure using the reddening of the iron shell as an indicator was sometimes followed. Studies were universely made in an attempt to monitor theoretically the instantaneous thickness of the refractory walls and one approach of those studies will be presented below by way of example.
FIG. 1 is a diagram for explanation of the prior art analysis approach, wherein a refractory brickwork with a heat conductivity of k.sub.1 is designated 1a, a refractory brickwork with a heat conductivity of k.sub.2 is designated 1b, and an iron shell is designated 2. The point A shows the inside surface of the brickwork 1a with a temperature of T.sub.0 and the point B shows the boundary between the two brickworks 1a and 1b. The point C designates a specific point in the refractory brickwork 1b having a temperature of T.sub.2 and the point D designates the boundary between the brickwork 1b and the iron shell 2 having a temperature of T.sub.3. Reference symbols l.sub.1, l.sub.2 and l.sub.3 designate the A-to-B distance, the B-to-C distance and the C-to-D distance, respectively. It is obvious from FIG. 1 that the brickworks 1a and 1b are made of different refractory linings, conventionally chamotte brick for the former and carbon brick for the latter. If the heat conductivities k.sub.1 and k.sub.2 of the brickworks 1a and 1b are fixed and the one-dimensional heat flow across the thickness of the refractory brickworks 1a and 1b is constant, then the following simultaneous equations will exist: ##EQU1##
Since k.sub.1 and k.sub.2 are known and T.sub.0 can be regarded as the melting point (say, 1150.degree. C.) of iron, the remaining unknown values are l.sub.1, l.sub.2, l.sub.3, T.sub.1, T.sub.2 and T.sub.3. Where a temperature probe is inserted from outside the iron shell 2 so as to sense the temperature T.sub.2 at the point A with the given depth and the temperature T.sub.3 at the point D on the external surface of the refractory brickwork 1b, l.sub.3, T.sub.2 and T.sub.3 as well as l.sub.2 may be specified because of l.sub.2 +l.sub.3 being a value set in the stage of designing the refractory brickworks. The only unknown values are l.sub.1 and l.sub.2 which may then be evaluated from the above simultaneous equations. Accordingly, it is able to realize the degree of wear of the refractory brickwork 1a and the temperature at the boundary between the refractory brickworks 1a and 1b for prediction of wear.
While being available as a device for estimating the remaining thickness of the refractory brickworks, the above mentioned method has several disadvantages as follows: In the foregoing the heat conductivities k.sub.1 and k.sub.2 of the refractory brickworks are considered as constant. These brickworks are necessarily subject to high temperature conditions for a great deal of time and especially the inside brickwork 1a would have been considerably deteriorated with an attendant variation of its heat conductivity (k.sub.1). These serious phenomena were not taken into consideration in the past. Otherwise, T.sub.0 is considered as being stationary at 1150.degree. C. in the above discussion. However, should foreign matters originating from iron ore or coke be attached onto the inner surface of the refractory brickwork 1a, T.sub.0 would have fallen below 1150.degree. C. This is another serious problem. Provided that no hot metal has yet developed in the proximity of the furnace body, T.sub.0 may not reach 1150.degree. C. Contrarily, T.sub.0 may go far beyond 1150.degree. C. due to a back blast. Any mechanism for tracing such variations in T.sub.0 was not available in the prior art. Although it seems possible to increase the number of the temperature-measuring points across the thickness of the walls in order to enhance accuracy, this approach has the outstanding problem of how to determine or estimate the temperature T.sub.0 and thus great difficulty in monitoring accurately the wear of the refractory brickworks as long as it falls within the category of the prior art.